Car cranks but wont start.

140,000 miles- 4x4
I have been having this problem with my truck like for a month now. The car seems to crank but wont start.I of course started with the basic. Does it pass gas, yes, do I have spark, yes. I have done several things to see if I get lucky. Changed the spark plugs, chnaged distributor, chnaged fule filter, air filter. I checked the spark from spark plug #1 and I got spark I also checked the spark from the coil and I got spark I checked the fuel from the valve and I got fule from it even though I get fuel from the valve, might it still be the fuel filter that is causing my truck not to start? When my truck is on it makes like a noice on the fule tank people tell me that its because the fulel filter is working it makes like this "zz" sound.
I have been turning my truck on my putting some starting fluid in the front I dont know what that is called but the air filter leads to it I think its the throttle and whn I put the starting fluid, the truck starts right away.
I also noticed that my truck has been a little shakier thatn normal, also what I noticed is that since these problems had started, I notced the neddle that marks my gas on the dash board is a little shaky that needle was never shaky it was always still and I noticed that when these problem started the gas neeedle started shaking any suggestion please, what else can I check or repair. THANKS